Pultrusion can be defined as a process for producing reinforced plastic geometric shapes in a continuous length by pulling a resin impregnated fiber reinforcement through a forming and curing die. Pultrusion dates back to the early 1950's when it was initially used to form round bar stock for the fishing rod industry. The systems, method and apparatus for forming pultruded shapes remained at this level for several years until the late 1960's when improvements allowed manufacturers to form various structural shapes used in a number of applications including corrosive and weather resistant ladders, gratings, hand rails, hoods, walkway supports, and structural elements for buildings such as greenhouses and the like.
However, fiber glass reinforced plastics (FGRP) which are formed by pultrusion have proved difficult to coat. Electrostatic coating techniques have not been employed to coat pultruded filament reinforced plastics (FRP) as these products are usually manufactured from non-conductive components resulting in non-conductive products. Conductive components such as conductive fabrics or conducting resin systems may be used to impart conductivity to the pultruded articles but the incorporation of these components carries the disadvantages of high cost and/or an undesirable increase in the thermal conductvity of the profile. High thermal conductivity is extremely undesirable in products used in architectural applications such as window frame parts.
It is an object of the instant invention to increase the receptivity of the FGRP to electrostatically applied coatings by incorporating conductive wires or rovings into the FGRP without significantly affecting the thermal conductivity of the FEGRP profile.
It is a further object of the present invention to coat filament or fiber glass reinforced plastics containing conductive elements by an electrostatic painting process.